OK, details first: This is a '97 Chevy 2500 with a Vortec 350 and an 0411 PCM. PCM has been in the truck for ~30k miles and has been fine until recently. This all started about a month and a half ago when we had a week straight of torrential rains and the distributor took a dump. Replaced it, and she ran again, but then noticed my scan tool was saying 'open loop fault', turns out one of my O2's was just flat - dead. Replaced both front O2's, now goes into closed loop no problem. Now she runs better, no vacuum leaks, I've checked a half dozen times and verified distributor timing is spot on, but I have 2 problems and I'm not sure if they're related.
1: Start the truck, put it in gear (any gear) and it stalls. Give it a little throttle as soon as it drops in gear and it'll chug a bit then be fine. Once it's warmed up it rarely does this, mostly just cold start.
2. Ignition timing. it's as if it's in some kind of 'limp mode'. Doesn't matter if I'm driving down the road part-throttle cruise, taking off from a light, flooring it, etc - it NEVER deviates from between 15* and 16* of ignition advance.
What gives? What would make the PCM do that with the timing? This seems to be the hardest question to answer, and all the tuners I've asked have no idea. So, here I am. Hopefully somebody here understands the 0411's ignition strategy and can point me in the direction of what could be causing this. Thanks for looking.